This invention relates to a method for calibrating a photographic image information of an original film such as a film negative used in a photographic printer in a case where the information of the image which is divided into picture elements is detected throughout the image.
With a photographic printer, it is generally necessary to measure a density amount of an original film such as a film negative for detecting the printing exposure amount or correction amount, and in the prior art technique of this field, a large area transmittance density (LATD) of the film negative is measured by photosensors, such as photodiodes, disposed near a light path of a printing lens unit. However, in the image detecting method by means of this LATD, the average density of the image of the film negative is measured and detected by the photosensors and the image density is not accurately detected entirely throughout the image surface, so that the printing exposure or correction cannot be correctly achieved. In the prior art technique, there has also been proposed a method in which the image surface of the film negative is divided into a plurality of equally aligned picture elements, the light passing through such elements are measured, and the densities detected in accordance with the measured light are corrected after the printing exposure amount has been determined. However, with this method, since the light measurement of the film negative is only approximately carried out, it is difficult to accurately detect information regarding the detail of the image of the film negative.
An apparatus for detecting the photographic image information developed for eliminating problems described above has been proposed by the same applicant, the detail of which disclosed hereunder with reference to FIGS. 1 through 4.
FIG. 1 shows one example of a photographic printer including the proposed detecting apparatus, in which a film negative 2 mounted on a film negative carrier 1 and conveyed to a printing portion is irradiated by a light source 4 through a filter means 3 consisting of three primary color filters of yellow (Y), magenta (M) and cyan (C). A light passing the film negative 2 is projected onto a photographic paper 7 through a lens unit 5 and a black shutter 6. The photographic paper 7 is wound around a supply reel 7A and wound up around a take-up reel 7B which is operated in synchronism with the conveyance and stoppage of the film negative 2 on the film negative carrier 1. Photosensors such as photodiodes 8 for detecting information regarding image densities of the three primary colors of red (R), green (G) and blue (B) are located near the lens unit 5 between the lens unit 5 and the film negative carrier 1 and a printing operation is carried out by signals detected by the photosensors 8. An image information detecting apparatus 10 is arranged near the film negative 2 in an inclined manner with respect to the light axis LS between the light source 4 and the film negative 2 on the film negative carrier 1. A lens unit 12 is located in front of a two-dimensional image sensor 11 for focusing the image of the central portion of the film negative 2. The two-dimensional image sensor 12 and the lens unit 11 are assembled in one unit as an image information detecting apparatus 10 on the rear surface of which is mounted a circuit board 13 to which a processing circuit such as an integrated circuit for processing the image is attached.
The two-dimensional image sensor 11 generally comprises a charge transfer device such as charge coupled device (CCD), and, as shown in FIG. 2, consists of an image detecting section 101 for optically pickup an image, a storage section 102 for storing electric charges transferred from the image pickup section 101 and an output register 103 for outputting the electric charges stored in the storage section 102. According to this construction, the two-dimensional image sensor 11 operates so that drive signals 101S to 103S from a driving circuit 20 control the sensor 11 so as to photoelectrically convert the image information of the two-dimensional area and to generate a picture signal PS which is output in a serial analog form from the output register 103. The circuit means mounted on the circuit board 13 is composed of, for example, the circuit as shown in FIG. 3, in which the image sensor 11 is operatively connected to the driving circuit 20 and is operated by the drive signals 101S to 103S from the driving circuit 20. The light irradiating upon the image pickup section 101 of the image sensor 11 is outputted from the output register 103 as a picture signal PS, which is then sampled by a sample-and-hold circuit 21 and held therein, and the sampled signal is then converted into digital signals DS by an analog-to-digital (A/D) converter 22. The digital signals DS from the A/D converter 22 is inputted into a logarithmic conversion circuit 23 to logarithmically convert the digital signals into signals DN representing the density of the image of the film negative 2 and the density signals DN are then written into a memory 25 through a write-in control circuit 24. In the control circuit 24, a signal RS representing the read-out speed for reading out at a constant speed the image information obtained by the image sensor 11 operated by the driving circuit 20 is preliminarily inputted and the density signals DN are written-in at the predetermined addresses in order of the memory 25 in response to the driving speed of the image sensor 11.
In the case of the usual photograph printing operation, according to the construction of the circuit means shown in FIG. 3, the light transmitted through the film negative 2 mounted on the film negative carrier 1 is detected by the photosensors 8 and then exposed on the photographic paper 7 with the exposure amount to be determined by the opening degree of the black shutter 6 based on the arrangement of the filter means 3 in response to the picture signals of the three primary colors R, G and B, respectively. The image information detecting apparatus 10 is arranged near the film negative 2 mounted on the film negative carrier 1 so as to detect the image information regarding a plurality of equally divided and aligned picture elements of the image throughout the whole film negative surface. In other words, since the two-dimensional image sensor 11 receives the light transmitted through the film negative 2 on the film negative carrier 1 through the lens unit 12 in accordance with the predetermined drive signals 101S to 103S from the driving circuit 20, the two-dimensional image sensor 11 divides the image of the film negative 2 into a plurality of aligned picture elements 21 as shown in FIG. 4A and sequentially scans the whole image of the film negative 2 in accordance with scanning lines SL. After the completion of the scanning operation, the picture signal PS is subsequently transmitted from the output register 103 of the image sensor 11 and sampled and held by the sample-and-hold circuit 21. The sampled signal is then converted into the digital signals DS by the A/D converter 22. The digital signals DS from the A/D converter 22 are logarithmically converted into the density signals DN in the logarithmic conversion circuit 23, which are then controlled by the write-in control circuit 24 and stored in the memory 25 in the aligned order corresponding to the picture elements 21 as digital signals regarding the density of the film negative 2 as shown in FIG. 4B. During the operation described above, it becomes possible to always correspond the divided element positions of the image of the film negative 2 to the data arrangement to be stored in the memory 25 by controlling the timing for writing the read-out speed signals RS received from the driving circuit 20 into the memory 25.
As described hereinabove, the digital values corresponding to the divided picture elements 21 of the picture image of the film negative 2 can be optionally read out from the memory 25 by storing therein the digital values of the picture elements of the film negative 2 or the density values of the picture elements of the three primary colors. Accordingly, if the density values of the three primary colors R, G and B are preliminarily stored as shown in FIG. 4B, the stored values can be read out and processed for example by operating or calculating the values, whereby the processed data can be utilized for determining the exposure amount or correction amount for the photograph printing operation as performed by the prior art method. In addition, since the two-dimensional image sensor 11 can detect the image information of the divided picture elements of the whole image of the film negative 2, the image information can be entirely accurately detected. Since the image sensor 11 is composed of predetermined numbers of picture elements, the image can be physically divided in accordance with the numbers of the picture elements, the element numbers of the image to be divided can be changed in accordance with the read-out speed change in a case where the film negative 2 and the image sensor 11 are moved relative to each other.
However, since the image information (FIG. 4B) stored in the memory 25 is effected by the unevenness of the constructional elements of the image sensor 11, the shading of the light source 4 and the aberration of the lens unit 12, the information of the image of the film negative 2 will not be correctly exhibited. For this reason, when the information stored in the memory 25 is utilized as is, the information is directly subjected to such adverse effects as described above and a photographic image with a good image quality cannot be obtained.